1. Field of the Invention
Elastomeric foam is used to insulate copper tubing. Stress corrosion, however, presents a special problem in this field. This corrosion, also known as stress corrosion cracking, starts with the formation of small intergranular cracks in copper tubing. Largely unnoticed and, therefore, unchecked, the condition which causes the development of the cracks eventually causes the cracks to propagate through the thickness of the copper tubing. The tube will either begin to leak or, dangerously and more seriously, the weakened tube can explode, allowing pressurized materials in the tube to escape violently.
The present invention offers a solution to the stress corrosion problem of copper tubing insulated with elastomeric foam and provides a specially formulated elastomeric foam for copper tubing. Since foam insulation is required to meet high fire retardancy standards, the instant invention is also concerned with elastomeric foam insulation which passes fire standards in addition to being copper-compatible. Preferred embodiments of the heat insulative foam are, therefore, presented which are particularly fire retardant.
2. Brief Description
In order to successfully retard copper oxidation and eliminate or reduce stress corrosion in the insulated copper tubing, a foam insulation is described herein which has been formulated to avoid the addition of phenol and ingredients which yield free phenol. This is a highly effective solution to the stress corrosion problem.
Stress corrosion has been found in the copper after the copper surface oxidizes rapidly. Factors which cause rapid copper oxidation and stress corrosion of copper are phenol, ammonia, and a high pH. Ammonia is present in all elastomeric insulations in at least small amounts. It forms during the process for making the foam when the blowing agent reacts to foam the product. The most feasible way to avoid stress corrosion, therefore, is to produce a phenol-free insulation or at least reduce the concentration of the phenol to a level which can be tolerated.
A copper-compatible elastomeric foam insulation comprises a foamed mixture of: rubber at 100 parts by weight, a vinyl chloride polymer in an amount of from about 15 to about 85 parts, a plasticizer selected from the group consisting of an alkyl phosphate ester and an oxyalkyl phosphate ester at an amount in the range of from about 10 to about 100 parts, at least about 100 parts of a fire retardant, a stabilizer at an amount up to about 10 parts, a preservative at an amount of from about 1.0 to about 10 parts, and a lubricant at an amount of from about 10 to about 85 parts by weight (wt.), wherein the foamed mixture contains no more than about 5 parts of free phenol per million.
By limiting the amount of free phenol in the insulation, contact with copper tubing can be maintained, but rapid copper oxidation and stress corrosion will be deterred. For this reason, the term "copper-compatible" is used to describe the insulation and compositions from which the insulation is made.
The elastomeric foam insulation must also meet the standard requirements in fire retardancy and for flame spread and smoke. Another problem is encountered in meeting fire standards because one cannot include aryl or arylalkyl phosphate ester plasticizers, since ingredients of this nature (containing aryl moieties) will, as a general rule, increase the amount of the free-phenol beyond the tolerance level. This can either be due to the release of phenol from the compound itself, or due to phenol impurities that can be inherent in the ingredient when added. However, without the aryl-containing phosphate plasticizers, the insulation normally has a flammability level that is too high to meet the required flammability standards.
Preferred embodiments, therefore, contain other additional ingredients which allow the copper tube insulation to meet required flammability standards. Accordingly, such embodiments will include ingredients such as char forming agents (char formers), flame retardants, and chlorinated lubricants. These ingredients allow foam insulation to meet flammability standards even if it is formulated with alkyl phosphate esters and does not contain the aryl phosphate esters.